One thing to be aware of for Reddit (and perhaps HN) is there are multiple scrapers archiving it in real time, so even if you delete a post from the main site it's still going to be available to anyone who takes the time to look. I would assume that government agencies archive and index all of that low hanging fruit as well.
I would think this is true though admittedly I think 95% of people just want their comments deleted so co-workers/friends can't stumble upon a semi-political hot take from a few years ago. Not because there is anything illegal or even career ruining.
